Ethylbenzene, C8H10, is a key raw material in the production of styrene and is produced by the ethylation reaction of ethylene, C2H4, and benzene, C6H6, in a catalytic environment. When sold as a commodity product, the product will usually contain at least 99.95 weight percent of ethylbenzene based on the weight of the product.
A source of benzene is reformate, which is prepared by contacting a mixture of petroleum naphtha and hydrogen with a reforming catalyst containing a support, e.g., halogen-treated alumina or non-acidic zeolite L, and a hydrogenation/dehydrogenation metal, e.g., Group 8, 9, or 10 metal such as platinum. That process typically produces a reformate that includes C5− hydrocarbons, C6-C8 aromatic hydrocarbons, e.g., benzene, C9+ hydrocarbons, C6+ paraffins, and cycloparaffins (naphthenes).
Another source of benzene is the cracking of hydrocarbons such as by steam cracking or catalytic cracking. That process typically produces an effluent that includes C6-C8 aromatic hydrocarbons, e.g., benzene, C6+ paraffins, and naphthenes.
Still another source for producing aromatics is the dehydrocyclo-oligomerization of C2-C5 aliphatic hydrocarbons. That process typically produces a product effluent that includes C6-C8 aromatic hydrocarbons, e.g., benzene, C6+ paraffins, naphthenes and C5 aliphatic hydrocarbons.
Benzene can be separated from other reformate hydrocarbons, e.g., C7+ aromatics, by distillation. However, the benzene obtained by distillation will usually contain C6 and C7 non-aromatic hydrocarbon impurities that are difficult to separate from benzene by distillation because they have boiling points close to the boiling point of benzene, i.e., their boiling point is within 10° C. of benzene (boiling point of 80.1° C.) at a pressure of about 101.3 kPa-a (absolute). This feed may also contain C5 paraffins and naphthenes, such as n-pentane and cyclopentane. These impurities, which are hereinafter sometimes referred to as “benzene coboilers”, may be present in the distillate product in an amount up to 75 percent by weight based on the weight of the product. Examples of benzene coboilers include cyclohexane, methylcyclopentane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 2,4-dimethylpentane, and dimethylcyclopentane.
The presence of these impurities during the ethylation of benzene can result in an ethylbenzene product having less than desirable purity. For example, the presence of benzene coboilers during the ethylation of benzene can result in the formation of ethylbenzene coboilers (hydrocarbons having a boiling point within 10° C. of the boiling point of ethylbenzene [boiling point of 136° C.] at a pressure of about 1 atm) that can not be easily removed from the ethylbenzene product by distillation. It is well known, e.g., disclosed in U.S. Pat. Nos. 5,258,569 and 5,221,777, that ethylbenzene coboilers can be formed by isoparaffin/olefin alkylation reactions.
Because of the deleterious effect of benzene coboilers, benzene obtained by distillation usually undergoes an additional step, i.e., extraction such as liquid extraction or extractive distillation, to remove benzene coboilers from the benzene product before the benzene is ethylated to form ethylbenzene. Generally, benzene used in the ethylation of benzene to produce high purity ethylbenzene has a purity of about at least 99.985 weight percent by weight based on the weight of benzene present in the benzene distillate. However, the extraction step is expensive and time consuming, which results in increased costs in manufacture of high purity ethylbenzene.
By the present disclosure, a process is provided for ethylation of benzene to produce high purity ethylbenzene that uses feed containing benzene that has not undergone extraction.